1. Field of the Invention
The present invention relates to pulsed oscillators such as those used in electronic sensors, like radar sensors utilizing pulse-echo range gating for target motion detection.
2. Description of Related Art
Continuous Wave CW Doppler radar motion sensors emit a continuous wave carrier and mix the transmitted radio frequency RF with the return echoes to produce a difference frequency equal to the Doppler shift produced by a moving target. CW Doppler sensors have a number of serious deficiencies that limit their widespread application: 1) lack of a definite range limit, which leads to false triggers on distant clutter, 2) high current consumption due to CW operation, making battery operation impractical, and 3) inability to collocate sensors due to mutual interference.
Amplitude Modulated AM, or pulse, Doppler motion sensors have been described in U.S. Pat. No. 4,197,537 by Follen et al., in U.S. Pat. No. 5,682,164 by McEwan, and others. In pulse Doppler, a short pulse is transmitted and its echo is mixed with either the transmitted pulse or a local oscillator such that either the pulse timing or its width defines the range gated region. With 100% amplitude modulation, response beyond the gated region is zero, eliminating false alarms from distant objects. Pulse Doppler motion sensors have many desirable attributes, but the prior art fails to teach low-cost high-performance embodiments for the higher microwave frequencies. Clearly, there is a need for a practical implementation at the higher microwave frequencies where compact directional antennas can be employed, and where more spectrum is available. The pulsed RF oscillator and detector of the present invention resolve these prior limitations.